Heat exchanger with imbricated bundles of exchange tubes



P. LEGRAND Sept. 10, 1968 HEAT EXCHANGER WITH IMBRICATED BUNDLES OFEXCHANGE TUBES Filed Oct. 18, 1965 2 Sheets-Sheet 1 Sept. 10, 1968 P.LEGRAND 3,400,759

HEAT EXCHANGER WITH IMBRIGATED BUNDLES OF EXCHANGE TUBES Filed Oct. 18,1965 2 Sheets-Sheet 2 United States Patent 3,400,759 HEAT EXCHANGER WITHIMBRICATED BUNDLES 0F EXCHANGE TUBES Pierre Legrand, 98 Rue de Rennes,Paris, France Filed Oct. 18, 1965, Ser. No. 497,039 9 Claims. (Cl.165-173) ABSTRACT OF THE DISCLOSURE This invention relates to a heatexchanger comprising a compact nest of straight and parallel exchangetubes disposed along the nodes of a centered hexagonal lattice, saidtubes being distributed among imbricated elementary bundles havingparticular connections with their headers and each consisting of atleast three tubes spaced from each other by pairs by a distance V3timesthe side of one mesh of the lattice.

The present invention primarily relates to a heat exchanger pertainingin particular to the type comprising a compact nest of straight andparallel tubes in which circulates a first fluid and about whichcirculates a second fluid preferably in a counter-flow direction.

When, for some reasons, one must dispense with tube plates whichconventionally collect the many ends of such tube bundles, one iscompelled for manufacturing and mounting reasons, in particular toprovide access to the welds, to avoid the separate connection of eachtube to its header; therefore, one is led to locally arrange in groupsthe adjacent tubes of elementary clusters, so that the number ofconnections to the header is reduced to a sub-multiple of the. totalmember of tubes in proportion of the number of tubes composing eachelementary nest, bundle or cluster.

The tubes being in general distributed over the crosssection of theexchanger in a regular manner and at equal distance from each other, forexample along the nodes of a centered hexagonal lattice, 'it could haveseemed advantageous that every ,elementary nest or bundle order tominimize the length of the internal connections of said elementary nestor bundle; moreover, itis advantageous that the tubes so arranged bedistributed in a pattern such that all the tubes of the exchanger may bearranged Now, in use, one may be led to cut off the circulation of fluidwithin one or several elementary nests, bundles or clusters and this fortwo reasons:

At first, one is'led to definitively shut off the circulation of fluidwithin a tube which has begun to leak. In a not veryclosely packed tubenetwork system, this maybe simply obtained by cutting or severing andobturation of the tube involved; in a close-packed tube network systemhowever, these operations are practically rendered impossible due to thedifiicult access to thetube involved; yet, since the tubes are arrangedin elementary nests or bundles, which alone are connected to the header,it

'remains the possibility to cut definitively off the circulation offluid in the elementary nest comprising the failing tube upon breakingits connection to the header.

Secondly, one may be led to temporarily out off the circulation of fluidwithin a significant fraction of the total number of tubes in theexchanger when these latter consists of a number of immediately adjacenttubes, in

ice

are arranged in independent sets each one connected to its proper headeror headers, as is the case, for safety reasons, with heat exchangers ofa very large bulk integrated in nuclear reactors.

The interruption of the circulation of internal fluid in an elementarynest or bundle involves two detrimental local consequences, the one ofthermal character and the other of mechanical character.

The first drawback is due to that the external fluid which circulatesabout the separate elementary nest or bundle, does not give off its heatand therefore forms a longitudinal column or sheet of fluid at asubstantially constant temperature, constituting a thermal shunt. Thisresults in a decrease of the overall etficiency of the exchanger.

The second drawback is involved in the local temperature distortionsattending the aforesaid thermal shunt and producing mechanicaldistortions between adjacent tubes, which is detrimental if theconnections between tubes are short and lack flexibility.

A first approach to the solution of these problems has been suggested inthe US. application Ser. No. 149,928, filed Nov. 3, 1961, now 'PatentNo. 3,249,154, issued May 3, 1966, wherein there are provided exchangertubes fitted with an axial core and with inner and outer helicalprojections which determine at any point for a minimal powerexpenditure, the circulations of fluids, respectively enabling thecentrifugation of the internal fluid and the constant transversediffusion of the external fluid, thereby tending to render thetemperature distribution homogeneous within the exchanger tubesthroughout the exchanger, thereby preventing the formation of theaforesaid longitudinal thermal shunt.

The presence of a core and of the inner helical projections reduces thecross-sectional area of flow left to the internal fluid; owing to thecross-sectional continuity, the connecting tubes are thereforenecessarily of a diameter substantially less than that of the exchangertubes and therefore have some flexibility to compensate for thedilferential expansions between adjacent tubes.

The object of the present invention is to completely remove theaforementioned drawbacks and may be advantageously combined with thesolution stated hereinabove and described in the previously mentionedpatent.

A heat exchanger according to the invention, pertaining in particular tothe kind wherein the exchanger tubes are arranged at the nodes of alattice having centered hexagonal meshes and wherein the adjacent tubesare locally arranged to constitute elementary nests, bundles or clustersprovided with their particular connections with their headers,collectors or manifolds, is more particularly characterized in that eachone of said elementary nests, bundles or clusters consists of at leastthree tubes which are not immediately adjacent to each other, and

which are spaced from each other by a distance 3 times the side of onemesh of the lattice and located the one at the center of such a mesh andthe others on the bisecting lines of at least two distinct sides of saidmesh.

According to another feature of the invention, said elementary nests,bundles or clusters are imbricated in such a manner that anyone tube ofa bundle is immediately surrounded by six tubes belonging to otherbundles.

According to still a further feature of the invention, said bundles orclusters are arranged in parallel rows.

According to still another feature of the invention, the successivebundles or clusters of a same row are connected to different headers ormanifolds according to a circular permutation.

'It at once results from the preceding arrangements that in an exchangerconstructed according to the method of the invention, the interruptionof the circulation of internal fiuid, whether it is definitive in asingle bundle or cluster or temporary in a set of bundles or clusters,cannot give rise to any longitudinal thermal shunt of significantimportance.

According to an embodiment enabling to put the invention into practicein a particularly convenient manner, said elementary bundles or clustersconsist of tubes arranged in a sheet or layer, that is located in a sameplane.

Further features, objects and advantages of the invention will becomeapparent as the following detailed description proceeds, illustrating byWay of example an embodiment with reference to the accompanyingdrawings, wherein:

FIGURE 1 is diagrammatic view showing an embodiment of arrangingexchange tubes of a heat exchanger into nests, carried out according tothe invention, this view substantially being a cross-section withrespect to the various tubes;

FIGURES 2 and 3 are general schematic diagrams showing how the tubes ofthe nests or bundles shown in FIGURE 1 are arranged and connected to theheaders or manifolds of their respective sets;

FIGURE 4 is an elevational view drawn to a larger scale, showing anelementary nest r bundle of the type used in the preceding figures;

FIGURE 5 is a cross-sectional view drawn to a larger scale and withparts broken away, taken at the level of line VV of FIGURE 4 showing thetubes of some nests or bundles arranged side by side and imbricated,pertaining to the type illustrated by FIGURE 4.

According to the embodiment shown in FIGURES 1 to 3 of the drawings, ithas been assumed that the tubes of the exchanger are arranged at thenodes of a lattice having centered hexagonal meshes. In FIGURE 1, fourhexagonal meshes formed by such tubes have been shown and denoted 1 to4. The tubes of these four meshes (which tubes are seven in number forevery mesh) have been shown by dots or points. To avoid encumbering thedrawing, the other tubes of the nest or bundle have not been shown ingeneral.

According to the invention, the various tubes of the exchanger have beenarranged in elementary nests or bundles of seven aligned tubes. Such anest or bundle of seven tubes, designated at 5, has been shown with itsseven tubes designated 6 to 12, respectively. Tube 12 is the mostcentrally located one of the elementary nest or bundle. To simplify thedrawing, the other similar elementary nests or bundles of the exchangerhave been designated only by their central tube such as 13, 14 or 15 forexample, surrounded on each side by lines representing the approximativesize of the three tubes adjacent to each central tube of each elementarynest, bundle or cluster.

Moreover, in the example shown hereinabove, it has been assumed thateach elementary nest or bundle of seven tubes belongs to one of the foursets of tubes and to distinguish these sets, a proper conventional signor mark has been used for differentiating them, viz: a triangle, asquare, the sign 1 or the sign x, respectively. Each one of these setshas its proper headers or manifolds which are arranged with each set.

Having thus specified the symbols used in FIGURE 1, it is seen that theexchanger may in addition be considered of being made from thejuxtaposition of blocks such as designated by 16, 17 and 18, of asubstantially rectangular general shape, consisting themselves of thejuxtaposition of elementary nests or bundles of seven tubes. Amechanical construction made from elementary blocks thus assembled is ofcourse very practical.

If one considers now anyone of the hexagonal meshes 1 to 4, one can seethat any one tube of the exchanger, that is for example the central tube19 of mesh 3, belonging to the set symbolized by a triangle, isimmediately surrounded by six adjacent tubes 20 to respectively,belonging to the other sets (tubes 20 and 23 belonging to the setsymbolized by the sign x, tubes 21 and 25 belonging to the setsymbolized by the sign 2 and tubes 22 and 24 belonging to the setsymbolized by a square). It may be understood that under thesecircumstances, no significant thermal shunt is to be feared whether oneis led to interrupt the circulation in an elementary nest or bundle oreven in a whole set of tubes of the exchanger.

This is made possible according to the invention by selecting a spacingbetween two tubes of a same elementary nest or bundle equal to /3 timesthe side of the mesh of the lattice used and by constituting eachelementary nest or bundle with at least three tubes one of which islocated at the center of one mesh of the lattice and the others on thebisecting lines of at least two distinct sides of said mesh. Thearrangement of elementary nests or bundles in seven aligned tubes is aparticularly convenient embodiment of the invention. However, thearrangement of the tubes in star-shaped elementary nests or inelementary'nests arranged in a herring-bone pattern, complying with thearrangement the formation of which has been set forth in the precedingparagraph, is quite usable for the objects of the invention.

The positioning of each block or pack of tubes such as 16, 17 or 18,consisting of adjacent elementary nests or clusters of seven tubes (suchas 5) is carried out by simply successively imbricating these nests orclusters.

In FIGURE 2 have been shown the connections between each nest of tubesand more specifically between each central tube of said nests and theirrespective headers or manifolds. Thus, one may see the connection withfour headers, collectors or manifolds 26 to 29, belonging to the setssymbolized by the signs 1, square, triangle, x, respectively, of thevarious central tubes of the elementary nests shown in the precedingfigure. Thus, notably, the tube 21 is connected to header 26, the tube22 is connected to header 27, the tubes 19, 12 and 13 are connected toheader 28 and the tube 23 is connected to header 29.

In FIGURE 3, the blocks 16, 17 and 18 of the preceding FIGURES 1 and 2,have been diagrammatically shown in an elevational view illustrating thepositioning of the tubes, of the water and steam headers and of thevarious connections. Thus, the tubes 6 to 12, of nest or bundle 5 areconnected to the water header 28 and to the steam header 28 by theircentral tube 12. At 30 has been shown the supporting core or Web of theblock or pack 16. It must be pointed out that the steam headers areresiliently supported by their tube connecting them with the variouscentral tubes of the elementary nests or bundles. It is seen that thesuccessive nests or bundles of a same block or pack or of a same rowsuch as 16, 17, 18 are connected to the various headers 26 to 29, 26' to29, through a circular permutation, in other words, starting from anybundle connected to a determined header, the successive bundles in thesame row are respectively connected to the other headers along apredetermined order until all the headers are used, and the samearrangement is repeated starting from the next bundle in the row. Thevarious headers connected to the elementary nests or bundles are in turnhierarchically arranged in successive collectors of increasing diameter(not shown) yet keeping within each arrangement the individual characterof each set. In the interesting case Where the main water inlet andsteam outlet headers must extend through the lower bottom of theexchanger, the aforesaid arrangements within each set of headers arecarried out, for the steam, either at the top or at the bottom of theexchanger and in this latter case, the four elementary headers of eachblock or pack (such as 16) extend separately down for example on theperiphery of the block involved wherein some tubes have been omitted toenable such a downward extension while retaining the standardrectangular contour of the block, allowing accurate juxtaposition ofsuch blocks.

In FIGURES 4 and 5 of the drawings, one has shown in a precise mannerhow may be constituted an elementary nest or bundle of seven tubes ofthe type used in the preceding FIGURES 1 to 3 and how such nests couldbe mounted in an imbricated fashion.

The nest or bundle shown in FIGURE 4 may be for example the nest orbundle 5 of the preceding figures. It is clearly seen that the centraltube 12 is flanked on either side by three adjacent tubes 6 to 8, and 9to 11, respectively. These tubes advantageously consist of the exchangetubes previously mentioned and described in the aforesaid patent.

Thus each elementary nest or bundle 5 is somewhat in the form of a flatseven-branched candlestick which for example is supported by means of aflange or collar 31 at the bottom part of the central tube 12, thisflange being adapted to be supported in turn by the web (FIGURE 3). TheWeb 30 rests upon a grid or grate 35 which lies on bearers 36 withrolling heads, which in turn rest on the ground 37.

In FIGURE 5, one can see in a precise manner how the central tubes (suchas 12, 32 to 34) of the separate nests or bundles have to be pinched anddeformed at their junction with the other tubes of the nest or bundle,so as to enable the positioning of the various elementary nests orbundles of tubes without any loss of space within the exchanger.

The side tubes 6 to 8 and 9 to 11 are kept on two extensions 38, 39 ofthe central tube 12. These extensions are made from tubes of largethickness and formed to this end with extruded portions 40 to and 46 to51 which are opposite by pairs and arranged on three levelsrespectively. To increase the compactness of the exchanger, theextensions 38, 39 in the area of the extruded portions have a flattenedrectangular cross-section.

The verticality of the self-supporting elementary nests or bundles isprovided by the lateral holding of the upper headers connectedthemselves by horizontal rods which in turn are either integral withstationary structures or \abutted upon the latter.

The invention is of course not at all limited to the embodimentdescribed and shown which has been given by way of example only.

What I claim is:

1. A heat exchanger, of the type comprising a closepacked nest ofsubstantially straight and parallel tubes disposed at the nodes of alattice having centered hexagonal meshes, wherein the adjacent tubes arelocally arranged to form separate elementary bundles having theirparticular connections with their headers, characterized in that eachone of said elementary bundles consists of at least three tubes spacedfrom each other by pair's by a distance 3 times the side of one mesh ofthe lattice and located the one at the center of such a mesh and theothers on the bisecting lines of at least two distinct sides of saidmesh.

2. An exchanger according to claim 1, wherein said elementary bundlesare so imbricated that anyone tube of a bundle is immediately surroundedby six tubes belonging the other bundles.

3. An exchanger according to claim 2, wherein said bundles are arrangedin substantially parallel rows or packs.

4. An exchanger according to claim 3, wherein the successive bundles ofa same row are connected to differing headers according to a circularpermutation.

5. An exchanger according to claim 2, wherein said elementary bundlesconsist of tubes located in a same plane.

6. An exchanger according to claim 5, wherein saidbundles comprise seventubes, viz. a central tube and six lateral tubes connected to the firstone by their ends.

7. An exchanger according to claim 6, wherein the connections betweenthe corresponding ends of said lateral tubes and of said central tubeare made by means of bent connecting tubular members having a diameterless than that of said tubes and comprising flared end portions, theends of said central tube comprising radial extrusions and thecorresponding ends of said lateral tubes terminating in a swagedportion, the diameter of said extrusions and swaged portionscorresponding to that of said flared end portions of said connectingtubular members.

8. An exchanger according to claim 7, wherein said central tubecomprises at each end an extension of greater thickness with asubstantially rectangular cross-section in which are provided saidextrusions.

9. An exchanger according to claim 8, wherein the lower extension ofsaid central tube comprises a reduced portion forming an outer shoulderwhereby the bundle is supported by support means integral with thestructures of the exchanger.

References Cited UNITED STATES PATENTS 3,104,652 9/1963 Tilleguin et al12232 3,249,154 5/1966 Legrand l64 FOREIGN PATENTS 640,772 4/ 1962Canada. 1,272,920 8/ 1961 France.

ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner.

